Sphere lapping machine



Nov. 26, 1963 H. N. HARMON 3,

SPHERE LAPPING MACHINE Filed Aug. 1, 1962 s Sheets-Sheet 1 & 4o

INVENTOR.

HUBERT N. HARM ATTORNEY Nov. 26, 1963 H. N. HARMON 3, 89

SPHE

Nov. 26, 1963 H. N. HARMON 3,111,789

SPHERE LAPPING MACHINE Filed Aug. 1, 1962 5 Sheets-Sheet 3 8 m N h 9 m o l I 1 l l p o m P H 2 g g I a I I (D 3 g i Q m 10 I E In i mfl L/ l I P 2 g l 5 Q 5 11 8 g a g m m 0 g g 0 sis: 9 I 2 2 I 9 Q m IO I m s 0 w L 4): w I

8 INVENTOR.

HUBERT N. HARMON W ATTORNEY United States Patent 3,111,789 SPEERE LAPPING MACHHNE Hubert N. Harmon, St. Paul, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Filed Aug. 1, 1962, Ser- No. 214,066 Claims. (Cl. 51-73) This invention relates to means for automatically producing spheres having a sphericity far in excess of anything commercially obtainable, even by the most careful nonautomatic processes. The need for rotors which are spherical within a very few millionths of an inch arose in connection with ultra precise gyroscopes for inertial navigation. The rotor must be spherical to a high order and sphere grinding methods hitherto satisfactory were found hopelessly inadequate for producing rotors meeting the more stringent requirements.

Recourse was had to hand lapping of spheres in concave laps, by operators having great skill and long experience, but this was far from satisfactory. Working to such accuracies was found to be an art rather than a science, and one that is not consistent with the best o-perators, while being entirely obtainable by many skilled machinists. Moreover, the time required to produce a single sphere by such methods was in excess of 200 manhours for the final lapping alone.

By the use of my invention, on the other hand, spheres have been produced automatically of such perfection as to require a minimum of hand lapping. The high accuracy is due in part to the fact that lapping pressure is maintained uniform to a degree which is impossible with human operators, and in part due to the fact that the path of the lap over the sphere is randomized to make sure that every portion of the sphere is lapped equally.

An object of the invention is to provide means for automatically producing spheres of an extremely high sphericity, accurate diameter, and perfect balance.

Another object is to provide means for rotating a sphere about its center in a statistically random pattern relative to a concave lap.

A more specific object is to provide means for alternately rotating a sphere about first and second intersecting axes while maintaining it in engagement with a concave lap having complex rotation about two further axes, neither of which coincides with either of the first two axes, but both of which pass through the point of intersection of the first two axes.

Yet another object is to provide a sphere lapping machine wherein the sphere to be lapped is transferred between two work holders which rotate about axes which intersect at the center of the sphere, while maintaining the center of the sphere in the same position.

:Various other objects, advantages, and features of novelty not individually enumerated above which characterize my invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects attained by its use, reference should be had to the subjoined drawing, which forms a further part hereof, and to the accompanying descriptive matter, in which I have illustrated and described a preferred embodiment of my invention.

In the drawing FIGURE 1 is a front view of an embodiment of the invention,

FIGURE 2 is a central longitudinal section of one of the work holders shown holding a workpiece, the section being taken parallel to the plane of the paper in FIG- URE 1,

FIGURE 3 is a schematic showing of electrical and pneumatic connections to the apparatus of FIGURE 1,

3,111,789 Patented Nov. 26, 1963 ice FIGURE 4 is a diagram showing one program for the work holder motors and valves of FIGURE 3, and

FIGURE 5 shows a modification of the structure shown in FIGURE 2.

As shown in FIGURE 1, the apparatus comprises a base plate 10 supporting a column '11 on which is secured in any suitable manner a headstock :12 carrying a shaft 13 in suitable bearings, not shown, for rotation about a vertical axis. A drive pulley 14 is carried on the top of shaft .13 for receiving a V-belt 15 driven by a suitable motor, and a pair of bevel gears '16- and 17 are rigidly mounted on the lower end of headstock :12 in spaced relation to one another. Headstock 112 may include a quill if desired to permit axial movement of shaft 13, as is conventional in drill presses.

Mounted on the lower end of shaft 12 by any suitable means such as a clamp screw 20 is an arm 21 carrying a second shaft 22 in bearings 23, for rotation about an axis which intersects the axis of shaft 13 at point 24. At its upper end shaft 22 carries a pair of bevel gears 25 and 26. Gear 25 is shown as engaging gear 117, but it may be shifted axially on shaft 22 to disengage gear 17, and gear 26 may be shifted axially on shaft 22 to engage gear 16. Thus as shaft 13 rotates arm 21, shaft 22 may be caused to rotate about its own axis at either of two speeds, while that axis is revolved as a Whole about the axis of shaft 13.

A lap 27 is mounted for axial adjustment in a clamp ring 28 forming a part of a lap carrier 30 on the lower end of shaft 22. Lap carrier 30 further comprises a gimbal ring 811 connected to clamp ring 28 by a pair of aligned screws 32 for pivoting about the axis of the screws. Ring 61 is pivoted, by further aligned screws 34, in a yoke 35 mounted for rotation with shaft 22, but capable of axial movement with respect thereto. A spring 36 urges yoke 35 in a downward direction.

Lap 27 comprises a short hollow cylinder of cast iron or other suitable material, the central bore of which may be of greater or less diameter to leave a lapping surface which is formed concavely to a spherical outline, and which may be grooved to carry or distribute lapping slurry. The diameter of lap 27 may be less than that of the sphere being lapped, depending on the lapping effect desired. The radius of the concavity is substantially that of the sphere being lapped, which is supported with its center located at point 24 by means about to be described, and which is indicated in FIGURE 1 by the broken circle 33.

Mounted on base plate 10 are a motor block 37, a rear mounting plate 40 and a front mounting plate 41. A work table 42 is carried on pins 43 received in openings in the edges of the mounting plates, and a splash guard 45 is mounted by grommets 46, 47 through which pins 43 pass. Work table 42 has a central aperture containing a spacer ring 48 which has a central bore through which the sphere projects downwardly.

A pair of motors 50 and 51 are suitably mounted on block 37, and act through couplings 52 and 53 to drive a pair of identical work holders 54 and 55, all respectively, secured to mounting plate 40 by means including clamp rings 56 and screws 57. The work holders pass through splash guard 45, as better shown in FIGURE 2, and rotate about axes which intersect at point 24 and extend at about 35 to the vertical; shaft 22 is at an angle of about 30 from the vertical. Pneumatic connections 6%) and 61 are made to work holders 54 and respectively at portions thereof which do not notate.

FIGURE 2 is a central longitudinal section of work holder 55 on a somewhat larger scale. The work holder is seen to comprise a body 62 mounted in clamping ring 56 and formed with a central bore 63 and a lower cylindrical chamber 64 with an annular upper recess 65 connected thereto, the recess being separated from the bore by a narrow annular ridge 66 pierced by a radial slot 6 7. Pneumatic connection 61 communicates with recess 65 through a passage 70.

Received in body 62 is a plunger 71 having a first portion 72 fitting into bore 63 and a second portion 73 fitting in chamber 64. A plurality of O-ring seals 74, 75 and 76 are provided in suitable grooves in plunger 71. Portion 72 is provided with a groove at 77, in alignment with slot 6 7 in body 62, and the groove is connected with a central bore "78 in portion 72 by a passage '79. At least a portion of bore 78 is of reduced diameter to act as a restriction to air flow through the bore. Plunger 71 is extended beyond portion 73 to receive or comprise a portion of flexible connection 53, which permits axial movement of one of its portions relative to the other while still transmitting rotation.

A cup 80 is mounted on the end of portion 7 2 of plunger 71 which projects beyond body 62, by a set screw 81. The rim of cup 80 is grooved to accept an O-ring 82, and a film or diaphragm 83- of sheet rubber or other suitable material that may overlie the O-ring and be fastened to the cup by a tie wire 84- received in a groove 85. The cup is bored at 86 to provide a chamber 87 having a central rib 88, and splash guard 45 has reentrant rings 90 which project within the chambers to prevent fluid from gaining access to the inner portions of the work holders. Cup 89 is centrally bored at 91 to communicate with bore 78 in plunger "'71.

Cup 86* is so mounted on plunger 71 as to permit the assembly to move axially in body 62 through about .04 inch of travel and is shown in the position it assumes when vacuum is first applied at 61. A spring 92 located in recess 65 acts to resiliently urge the assembly in the direction of connection 53. Under suction, the ambient air pressure tends to force plunger 71 into body 62, moving the cup into contact with the sphere, which is held tightly to the cup by atmospheric pressure as the pressure in the cup decreases. The restriction in bore 78 acts to ensure that movement of plunger 71 takes place promptly and is then followed by reduction in pressure in the chamber. It has been found by practical experience that when the work holders are in use in filter 89 in the chamber of cup 80 may be used to prevent slurry from entering the central bore 78 and the diaphragm 83 may be omitted.

Work holder 55 is mounted in clamp ring 56 in such a position that when vacuum is applied and cup 89' is in its upward position, the surface of the diaphragm overlying ring 82 coincides with the small circle of a sphere of the desired diameter centered at 24 Work holder 54 is similarly adjusted. It will be seen that when vacuum is removed from either work holder it reverts to a position in which it does not quite contact a sphere supported by the other work holder. Thus means are pro vided for transferring the sphere from one work holder to the other while maintaining the position of its center unchanged.

In use the sphere being lapped is covered with a lapping slurry which may be a thousandth of an inch or more in thickness, so accuracy greater than this in mechanical consruction is unwarranted.

Reference should now be had to FIGURE 3 which shows an exhaust manifold 93 connected through three- Way solenoid valves 94 and 95 to pneumatic connections 60 and 61. In the deenergized condition, valves 94 and 95 port work holders 54 and 55 to the atmosphere: when energized the valves supply vacuum from source 93 to the work holders. The figure also shows a source 96 of electrical energy having a first conductor 97 connected to 'motor 51, valve 95, valve 94, and motor 50 and to a cycling motor 100, and a second conductor 1111 connected through a single pole double throw switch 102 either to motor 190 and to a plurality of switches 153, 104, 105 and 106 actuated by cams 167, 158, 115 and 4 111, respectively, on the shaft 112 of motor 100, or to a plurality of manually operable switches 113, 114, 115 and 116. Switches 163406 and 113-116 are connected to motor 51, valve 95, valve 94, and motor 59, all respectively.

The program of operation of FIGURE 3 under control of motor 1%, when switch 102. is thrown upwardly, is shown in FIGURE 4. Motor 101) is so arranged that shaft 112 rotates at a speed of one revolution per minute. Time zero seconds is defined as the point where valve 94 becomes energized: valve is also energized at this time, and motors 5d and 51 are deenergized. The sphere is held by both work holders. At time 1.5 seconds valve 95 is deenergized, leaving the sphere held by work holder 54 only. At time 3.4 seconds operation of motor 50 begins, rotating the sphere about the axis of work holder 54: after 3.8 seconds motors 59 is deenergized. At time 9.5 seconds valve 95 is energized so that the sphere is again held by both work holders, and at time 11.5 seconds valve 94 is deenergized, so that the sphere is transferred from work holder 54 to work holder 55. At time 14.5 seconds motor 51 is energized and the sphere is rotated about the axis of work holder 55: after 5.7 seconds motor 51 is deenergized. The cycle continues, the sphere being transferred from holder to holder and then rotated. All this time lap 27 is being continually driven in complex rotation about the axes of shafts 13' and 22, so that the lap engages the sphere and lapping takes place using a slurry applied to the sphere in any suitable fashion, as manually by means of a small brush.

The length of the period of rotation of the sphere beginning at time 3.5 seconds is shown as clearly shorter than the lengths of the other periods of rotation, which are all shown equal. For the short period the sphere rotates through an angle of about 146 degrees: for the other periods it rotates about 218 degrees. This is to prevent the sphere from following a simple path with respect to the lap, and thus insures that the lap engages every portion of the sphere in a controlled approximation of a random pattern.

It has been found that the effectiveness of the lapping procedure is influenced by the pressure exerted by the lap on the sphere being ground. To achieve a desired pressure a suitable size of Wire and pitch of convolution are used in spring 36. Minor adjustments may be accomplished by varying the position of lap 27 axially in clamp ring 28.

In using my apparatus the work pieces are spheres which are formed within the tolerances of conventional machining procedures. In user, a rough sphere of this sort is placed in the apparatus and lapped using the automatic program, being removed at intervals and tested for balance, sphericity, and diameter, until the latter two come within a predetermined range. The static mass unbalance at this time is noted. The automatic cycling is now interrupted by throwing switch 102 downward, the sphere is placed in the apparatus with its center of gravity vertically about point 24, the lap is replaced by one of somewhat smaller diameter, switches 114 and 115 are both closed to hold the sphere in fixed position, and lapping is continued for an interval determined by the magnitude of the unbalance. Switches 114 and 115 are then opened, the sphere is readjusted in the apparatus with its center of gravity on the axis of work holder 55 and toward the lap, the larger lap is replaced in the lap holder, and switches 114 and 113 are closed, lapping being continued for a further period, after which switch 102 may be thrown upwardly and programmed lapping may continue.

An incidental advantage of my apparatus which has been found to be of great practical value lies in the ease with which a sphere can be inserted for lapping and removed for measurement. Since these operations must be performed repeatedly, much time is saved by the capability for simply placing and removing the sphere without engaging and disengaging any mechanical connections.

Numerous objects and advantages of my invention have been set forth in the foregoing description, together with details of the structure and function of the invention, and the novel features thereof are pointed out in the appended claims. The disclosure, however, is illustrative only, and I may make changes in detail, especially in matters of shape, size and arrangement of parts, within the principle of the invention, to the fuli extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

I claim as my invention:

1. A sphere lapping machine comprising, in combination: work holding means :for supporting a sphere to be lapped with its center at a predetermined point lying on a first axis, including first and second holding members severally reciprocable along and rotatable about respective second and third axes which intersect each other and said first axis at said point; and lap actuating means including a lap having a concave spherical lapping surface, lap holding means reciprocable along and rotatable about a fourth axis passing through the center of said concave spherical surface, and means causing said fourth axis to revolve about said first axis while continually passing through said point.

2. A sphere lapping machine comprising, in combination: work holding means for supporting a sphere to be lapped with its center at a predetermined point lying on a first axis, including first and second holding members severally rotatable about respective second and third axes which intersect each other and said first axis at said point; and lap actuating means including a lap having a concave spherical lapping surface, lap holding means supporting said lap and rotatable about a fourth axis passing through the center of said concave spherical surface, and means supporting said lap holding means and causing said fourth axis to revolve about said first axis while continually passing through said point.

3. In a sphere lapper, in combination: means can-sing compound rotation of a concave spherical lap about both of a pair of axes intersecting at a point which is substantial'ly coincident with the center of the spherical surface of said lap; a pair of pneumatic sphere holders, reciprocable along and rotatable about separate [further axes which pass through said point for indenpendently supporting a sphere in engagement with said lap; motor means energizable to cause rotation of each of said sphere holders about the axis thereof; actuating means for reciprocating each of said sphere holders out of a normal position and into a position for holding a sphere with its center at said point; and program means controlling energization of said motor means and operation of said actuating means to cause interrupted rotation of a sphere in the lapper :alternately about the axes of said holders, whereby to bring all points on the surface of the sphere into the working area of the lap for substantially equal periods of time.

4. In combination: a cup-shaped member having an open end; means mounting said member for rotation about an axis and limited reciprocation therealong from a normal position; a flexible elastic membrane closing the open end or said member; motor means for causing said rotation of said member; means continuously providing a passageway to the inside of said member; a source of reduced pressure; and means interruptedly connecting said source to said passageway and energizing said motor means.

5. In combination: a pair of cup-shaped members; means mounting said members for rotation about a pair of intersecting axes and for limited reciprocation therealong from a normal position; drive means energizable to cause rotation of said members; means continuously providing passageways to the insides of said members; a source of reduced pressure; and means alternately connecting said source to said passage-ways and alternately energizing said drive means.

References Cited in the file of this patent UNITED STATES PATENTS 513,632 Conrader Ian. 30, 1894 2,688,220 Boutell Sept. 7, 1954 2,966,765 De Vore Jan. 3, 1961 

1. A SPHERE LAPPING MACHINE COMPRISING, IN COMBINATION: WORK HOLDING MEANS FOR SUPPORTING A SPHERE TO BE LAPPED WITH ITS CENTER AT A PREDETERMINED POINT LYING ON A FIRST AXIS, INCLUDING FIRST AND SECOND HOLDING MEMBERS SEVERALLY RECIPROCABLE ALONG AND ROTATABLE ABOUT RESPECTIVE SECOND AND THIRD AXES WHICH INTERSECT EACH OTHER AND SAID FIRST AXIS AT SAID POINT; AND LAP ACTUATING MEANS INCLUDING A LAP HAVING A CONCAVE SPHERICAL LAPPING SURFACE, LAP HOLDING MEANS RECIPROCABLE ALONG AND ROTATABLE ABOUT A FOURTH AXIS PASSING THROUGH THE CENTER OF SAID CONCAVE SPHERICAL SURFACE, AND MEANS CAUSING SAID FOURTH AXIS TO REVOLVE ABOUT SAID FIRST AXIS WHILE CONTINUALLY PASSING THROUGH SAID POINT. 